Fix bugs found by Dart analyzer

sky/sdk/example/rendering/sector_layout.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/sky_binding.dart';
@@ skipping 80 matching lines @@
     deltaRadius = constraints.constrainDeltaRadius(0.0);
     deltaTheta = constraints.constrainDeltaTheta(0.0);
   }
   void performLayout() {
     // descendants have to either override performLayout() to set both
     // the dimensions and lay out children, or, set sizedByParent to
     // true so that performResize()'s logic above does its thing.
     assert(sizedByParent);
   }
 
+  Rect get paintBounds => new Rect.fromLTWH(0.0, 0.0, 2.0 * deltaRadius, 2.0 * deltaRadius);

[Hixie, 2015/07/10 18:01:01]

this seems wrong. the origin is on the middle of the circle. this should
probably be from -radius-deltaRadius to radius+deltaRadius.

[abarth-chromium, 2015/07/10 18:09:30]

Ok.  Currently it's not used by anything because none of the sectors create
their own display list.

+
   bool hitTest(HitTestResult result, { double radius, double theta }) {
     assert(parentData is SectorParentData);
     if (radius < parentData.radius || radius >= parentData.radius + deltaRadius ||
         theta < parentData.theta || theta >= parentData.theta + deltaTheta)
       return false;
     hitTestChildren(result, radius: radius, theta: theta);
     result.add(new HitTestEntry(this));
     return true;
   }
   void hitTestChildren(HitTestResult result, { double radius, double theta }) { }
@@ skipping 374 matching lines @@
     if (radius < innerRadius)
       return false;
     if (radius >= innerRadius + child.deltaRadius)
       return false;
     if (theta > child.deltaTheta)
       return false;
     child.hitTest(result, radius: radius, theta: theta);
     result.add(new BoxHitTestEntry(this, position));
     return true;
   }
-  
+
 }
 
 class RenderSolidColor extends RenderDecoratedSector {
   RenderSolidColor(Color backgroundColor, {
     this.desiredDeltaRadius: double.INFINITY,
     this.desiredDeltaTheta: kTwoPi
   }) : this.backgroundColor = backgroundColor,
        super(new BoxDecoration(backgroundColor: backgroundColor));
 
   double desiredDeltaRadius;
@@ skipping 25 matching lines @@
   stack.add(new RenderSolidColor(const Color(0xFFFFFF00), desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(const Color(0xFFFF9000), desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(const Color(0xFF00FF00)));
   rootCircle.add(stack);
   return new RenderBoxToRenderSectorAdapter(innerRadius: 50.0, child: rootCircle);
 }
 
 void main() {
   new SkyBinding(root: buildSectorExample());
 }